From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6F6E82DB79F; Tue, 14 Jul 2026 16:31:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784046700; cv=none; b=A/QwEW7r0NTptFectAaWC3FtraMEsvZjdKfxZmX8fUD7EnIa+mq3OuQ15nB7AkIFui8EiKFtEl2czoJybgL9ZEvWeDjP39k/+rGaOk5g9jBohKZUqM8tlN9ibT+3iPgsl67V4rqq30FQacQneB+MEO6xZAsdKwUaktScofWFMF0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784046700; c=relaxed/simple; bh=ESLn5gYkBhn3MwOsdBDvzmrgF+HM9AfadUfTshdJrak=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=F9vTA3DxrlXh9I7S/XbpZqdjxGON7IwuTIMR8rydoU+fmvTTot7/GMF+UDEX2mdMFfeUhmvFGq3UWd95dl38RIzLUvmFZkyoW6PuV0UbGF13jdjnEWSqkOYHs47UcpzHnqRnlyvZ15UkEN86k+HZz6VlyMD8NWGZoTwKufJv28c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Iygubm95; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Iygubm95" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EAE6F1F000E9; Tue, 14 Jul 2026 16:31:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784046699; bh=eGNkPqfQ+3YiSeTrXQY7i4khsNfUcYyUJCaxbq5y5TI=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=Iygubm950SawUz4H6UdS1oHVtFGj3vmU5Xr/LNe8MPPQAgJoBBt0xoxlt4TBODD1z FNNjwb9hOZ311y07/ZAftU1hQEc34e8x+jf1tf6LYhhNd3YOXl7mnW2RqmBZyY4T7G wIUg312HE7PRBXrs/M9RpJL/bPN7IRFKS+RDRpl+ZcVJ1j3oJP1lm5I4awTNye4/VV 9g27mbKmIzZW3RD29yOpill2fYN+TUbPp7mIKoJaCEmsyGt1rlgtJ3t9xRpmfjLJnD 41ledS9h43TNXkoCOh2oY4bF/tj2duuTHZp8P4tYTasFzJKq1S0z9SI4PBQwBX30IQ jMGJ5R/NT8D4Q== Message-ID: <2d51a1ad-85be-46bf-ac36-18eca199b449@kernel.org> Date: Tue, 14 Jul 2026 18:31:22 +0200 Precedence: bulk X-Mailing-List: linux-csky@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 10/34] x86: mm: carve out the generic compile-time folded pgtable case in effective_prot() To: Yeoreum Yun , Dave Hansen Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linux-arch@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, x86@kernel.org, linux-mm@kvack.org, kasan-dev@googlegroups.com, linux-csky@vger.kernel.org, linux-m68k@lists.linux-m68k.org, linux-openrisc@vger.kernel.org, linux@armlinux.org.uk, akpm@linux-foundation.org, ankur.a.arora@oracle.com, rppt@kernel.org, linmag7@gmail.com, chleroy@kernel.org, klarasmodin@gmail.com, chenhuacai@kernel.org, kernel@xen0n.name, kas@kernel.org, zhangtianyang@loongson.cn, wangyuli@aosc.io, tsbogend@alpha.franken.de, ljs@kernel.org, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, arnd@arndb.de, ryan.roberts@arm.com, pasha.tatashin@soleen.com, rmclure@linux.ibm.com, baolin.wang@linux.alibaba.com, tj@kernel.org, kevin.brodsky@arm.com, anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org, palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, hannes@cmpxchg.org, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, kasong@tencent.com, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, ryabinin.a.a@gmail.com, glider@google.com, andreyknvl@gmail.com, dvyukov@google.com, vincenzo.frascino@arm.com, anshuman.khandual@arm.com, yang@os.amperecomputing.com, chaitanyas.prakash@arm.com, ardb@kernel.org, guoren@kernel.org, yang.li85200@gmail.com, viro@zeniv.linux.org.uk, dinguyen@kernel.org, schuster.simon@siemens-energy.com, wangruikang@iscas.ac.cn, junhui.liu@pigmoral.tech, muchun.song@linux.dev, vishal.moola@gmail.com, namcao@linutronix.de, pavel@kernel.org, djbw@kernel.org, yu-cheng.yu@intel.com, baolu.lu@linux.intel.com, Jonathan.Cameron@huawei.com, coxu@redhat.com, andreas@gaisler.com, liam@infradead.org, vbabka@kernel.org, surenb@google.com, mhocko@suse.com, geert@linux-m68k.org, shorne@gmail.com, jonas@southpole.se, stefan.kristiansson@saunalahti.fi References: <710b7eb0-8e0c-4f07-991c-2285c77e1beb@intel.com> <6007625e-c3f9-4ad6-99a8-61396bccbcec@kernel.org> <32d459d1-ad19-4baf-bbb1-0565458001d2@intel.com> <3ea30f8a-bb29-4bf5-8400-1c4840d46a88@kernel.org> <7e84b200-25eb-43a6-b5e2-5f27f2d82a77@intel.com> <31988089-095a-4eed-b5e2-c677c70f79f6@kernel.org> <14e250db-1641-4085-8d13-02f819657d5f@intel.com> <6df814c9-405c-48d8-96ea-929c4b28949b@intel.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >> This makes a *ton* of sense in effective_prot() especially. Its entire >> job is mirroring the hardware's job of inheriting permissions from >> higher levels of the page tables and enforcing them on lower level leaf >> entries. If a higher level is folded, there's nothing to inherit. >> >> I also think it's worth taking a brief pause on the coding to think >> about what kind of design would actually be nice here. If the design >> really is that the pgd is folded, the 'struct mm_walk_ops' code would >> ideally not even call ->pgd_entry(). It would just (for example) *start* >> at ->pud_entry() for a 3-level hardware page table. >> >> If there are no pgds, why bother calling ->pgd_entry()? It couldn't be >> done transparently to mm_walk users of course but it could be done >> incrementally where users move one at a time over to a new scheme. > > Agree. Calling a pXd_entry() about folded one seems meaningless. > But seems enough to check mm_pXd_folded() before calling pXd_entry() > in each walk_pXd_range(). Needs some double-checking that callers can handle it (like effective_prot() would currently not), but certainly something to look into! -- Cheers, David